The use of direct venting with fireplace inserts and fireplaces generally is well known. Direct venting separates the room air and the combustion air and is differentiated from venting typically known as "B-type" venting. In B-type venting, air obtained from the room is used for combustion. The air then exits the combustion chamber from a vent open directly to the atmosphere. In direct venting, room air is not used from combustion. Rather, air used for combustion is drawn into the combustion chamber by use of a vent which is exposed to the outside ambient air. A first duct connected to the vent conveys this outside air to the combustion chamber. After combustion, this air and the combustion byproducts are conveyed directly to the vent through a second duct which is isolated from the first duct. Typically, the two ducts are cylindrical and concentric with the inlet air being conducted to the combustion chamber through an annulus outside the exit air duct and the exit air being conducted to the vent by way of the inner duct. The room air is drawn from the room within which the fireplace is positioned and is then heated by way of a heat exchanger operably exposed to the combustion chamber. The heated air is returned to the room without direct exposure to the combustion chamber or the air of the combustion chamber. The safety advantages are significant and readily apparent.
Where there is no chimney present such as would usually be the case where the fireplace is located in the basement of a residence, the vent used for fireplace air inlet and air exit is typically located on the outside wall of the house being heated.
There are significant drafts present around the vent located on the wall of the house which affects the backpressure in the exit duct. If there is a good draft present that tends to draw the exit air from the exit duct, the fireplace will operate more efficiently. If there is backpressure present in the exit duct, the draw of inlet air will be reduced which will decrease combustion efficiency and can lead, in poorly designed systems, to extinguishing the combustion flame. This is undesirable.
The prior art vent typically used two flat plates located a distance away from the outlet of the exit duct. The inner flat plate; that is, the plate closest to the exit duct, was impacted by the combustion exhaust products. Because it thereby became heated, a second or outer flat plate of virtually the same dimensions was separated a distance from the first plate to prevent burns. A third plate with a centre hole was provided between the first plate and the outlet of the exhaust duct. The theory behind the use of the third plate is somewhat obscure but the center hole is of a greater diameter than the diameter of the outer inlet air duct and it is known that the use of the third flat plate assists in dissipating the exhaust air coming from the exhaust duct thereby reducing backpressure in the exhaust duct. A rectangular housing was connected on one side to the wall through a wood frame and on the opposite side to four (4) rods which extended through the flat plates. The housing had a series of elongate perforations extending therethrough to protect the inlet duct from negative drafts.
While the prior art side vent generally operates satisfactorily in most applications, the further distance the vent is from the wall of the house, the better the draft will be. The length can be such, in small sized property lots, that the end of the vent may extend over the property line of an adjoining residence. The use of the flat plate upon which the combustion gases impact does not assist in dissipating the exhaust gases and can cause the undesirable backpressure.